The present invention is directed to a support for a fill pump piston. More particularly, the present invention is directed to a support for a piston in a piston-type fill pump for use in a form, fill and seal packaging machine.
Form, fill and seal packaging machines are well known in the art. These machines are widely used in the food packaging industry for forming a package, filling the package with a liquid or solid food (or a mixture of liquid and solid foods), and sealing the package after filling. In many such machines, piston pumps are used to move or transport product (e.g., food product) from, for example, a storage tank to individual packages. Piston-type pumps provide for the requisite control over the flows and flow rates of the product.
In addition, in such machines, sterilization, generally, must be kept at a maximum. That is, all of the food or product contacting surfaces must be maintained at a high level of cleanliness in order to reduce the opportunity for product contamination. A number of processes and philosophies are carried out in such machines in order to maintain the requisite high levels of cleanliness. One such philosophy is to minimize the number of surfaces that contact the product, and particularly to reduce the number of moving surfaces, and close-moving mechanical surfaces that are product-contacting.
One primary example of this is in connection with the moving piston that is used to drive or transport the product. In one commonly used arrangement, a diaphragm is positioned between the piston and the cylinder wall to isolate the product from the close proximity piston and cylinder wall surfaces. In such an arrangement, the diaphragm, which is referred to as a rolling diaphragm, is positioned at the product end of the piston and extends to (and is sealed at) the cylinder wall. The diaphragm serves to substantially isolate the product from the space between the piston and cylinder wall where heat may be generated. The diaphragm also serves to isolate the product from the driver portion of the pump and other mechanical pump surfaces. Because the diaphragm is a flexible material, it “moves” with the pump and provides the necessary volumetric changes to allow moving or driving the product.
Although such an arrangement functions well to isolate the product from the moving mechanical components, because the diaphragm is positioned between the stationary cylinder wall and the moving piston, it is subject to wear by virtue of the rubbing of the surfaces. In addition, in the event that the piston is not aligned within the cylinder, there exists the potential for the diaphragm to rupture or otherwise fail prematurely (e.g., debraid, separate) as a result of the piston coming too close to the cylinder wall.
One way to overcome the potential for damaging the diaphragm by contact of the piston with the cylinder wall is to increase the gap between the piston and the cylinder by increasing the cylinder bore or decreasing the piston diameter. However, as the gap between the piston and cylinder wall increases, the volume of product moved (per pumping stroke) is subject to changes. This is problematic in that the volume of product pumped is a “measured” volume as such, the flow rate must be maintained at a precisely controlled rate. Moreover, as the gap increases, the overall support for the diaphragm decreases.
Accordingly, there exists a need for an improved alignment or centering system for a piston in a piston pump. Desirably, such a centering system reduces the opportunity for the piston to contact the cylinder wall and as such reduces the wear on the pump diaphragm. Most desirably, such a centering system does not add any frictional or other force that could adversely effect the ability to accurately dose the amount of product transferred during the pump stroke, nor does it reduce significantly the amount of product transferred during each pump stroke.